JP5098106B2 - Carbon nanotube reinforced polymer - Google Patents

Description

Detailed Description of the Invention

The present invention
a) contacting a carbon nanotube with an aqueous component that is at least partially a water-soluble first polymer or a water-soluble surfactant in an aqueous medium;
b) mixing the product obtained from step a) with an aqueous latex of the second polymer;
c) removing water from the mixture thus obtained;
d) heating the product from step c) to a temperature at which the second polymer flows; and e) a method for preparing a carbon nanotube reinforced polymer by the step of solidifying the product of step d) into the desired form.
Such a method is described in WO 2004/072159 pamphlet.

  In recent years, great efforts have been made to incorporate carbon nanotubes into polymer matrices. The resulting composite is an interesting material. Because they have enhanced electrical and mechanical properties at very low loadings due to unique nanotube properties (eg, high aspect ratio and electrical conductivity). However, dispersion of carbon nanotubes in high viscosity polymers is difficult and has often been attempted by functionalizing the nanotubes to provide attractive interactions between the nanotubes and the polymer. In addition, the dispersion of expanded nanotubes was a challenge because the nanotubes are highly bundled as a result of strong van der Waals interactions.

In general, materials can be divided into three groups with respect to their electrical conductivity δ: insulators (δ <10 ⁻⁷ S / m), semiconductors (δ = 10 ⁻⁷ to 10 ⁵ S / m) and conductors. (Δ> 10 ⁵ S / m). For intrinsically non-conductive polymers, typical conductivity values are 10 ⁻¹⁵ S / m to 10 ⁻¹² S / m. The carbon filler may have a conductivity in the range of 10 ⁴ S / m to 10 ⁷ S / m. In the composite, the conductivity is slightly lower than for pure carbon species with higher filler concentrations.

  Carbon nanotube reinforced polymers are currently made by incorporating carbon nanotubes (CNTs), generally produced in bundles, into a polymer matrix. In order to obtain a homogeneous distribution of these CNTs, the CNTs are pretreated by either sonication or chemical modification processes, which improves the dispersibility of individual CNTs in the polymer matrix. The purpose is to do. Such incorporation of CNTs into the polymer matrix is beneficial for enhancing the stiffness and conductivity of the polymer matrix material.

  It has been found that using the teachings of the prior art results in a significant change in conductivity when increasing the amount of carbon nanotubes. Since the transition is almost an S curve, it is difficult to control the level of conductivity between the original conductivity of the matrix and the final level of the enhanced product.

  It is necessary to be able to set the electrical conductivity value to a specific desired level (as described above for different conductive materials).

  Surprisingly, it has been found that a specific amount of low molecular weight fraction in the second polymer can control the level of electrical conductivity of the composite in a given amount of carbon nanotubes, which is the core of the present invention. is there.

  As a characteristic of the method of the present invention, the second polymer has both a low molar mass fraction and a high molar mass fraction, and the low molar mass fraction has a weight average molecular weight (Mw) of 500-20,000 g / mol. However, the high molar mass fraction has a Mw of 20,000 to 5,000,000 g / mol and the low molar mass fraction is present in the second polymer in an amount greater than 5 wt%.

  The method steps of the present invention are described separately below.

Step a): Step of preparing a slurry from carbon nanotubes in an aqueous medium This method is described in WO 02/076888. This publication describes a method of expansion of single-walled carbon nanotubes (SWNTs), resulting in a stable aqueous product comprising essentially a single tube. In this publication, a water-soluble polymer material is used to obtain expanded nanotubes. The contents of this publication are incorporated herein by reference. This method can also be applied when using multi-walled CNT (MWNT). In the method of the present invention, the use of SWNT is preferred.

  As described in WO 02/076888, the at least partially water-soluble polymeric material should preferably be hydrophilic and can be of natural or synthetic origin. See also WO 2004/072159 pamphlet. When improving hydrophilicity, it is advantageous to improve the uptake of at least partially water-soluble polymeric material, and to add an electrolyte such as a water-soluble salt (sodium chloride) (eg in this step a)). It is shown that there is. Thereby, the dispersibility of CNT in the matrix of a carbon nanotube reinforcement | strengthening polymer improves.

  Step a) can also effectively swell the CNTs using a water soluble surfactant. Hydrocarbon sulfates or sulfonates such as sodium dodecyl sulfate (SDS) or sodium dodecyl sulfonate are preferred. Polyalkylene oxide surfactants are also preferred.

  The method of step a) is performed by bringing essential components (polymer or surfactant and carbon nanotube) into contact in any order in water or an aqueous solution. The obtained product can obtain up to 75% by weight of carbon nanotubes and is covered with the first polymer or surfactant. In step a) of the method, the mass ratio of the first polymer or surfactant to the carbon nanotubes can range from 0.05 to 20.

  The temperature at which this step a) is performed is not critical. A temperature between room temperature and 75 ° C. is very well suited.

  The residence time required for effective expansion of the carbon nanotubes can be readily determined by those skilled in the art. For that purpose, a residence time of less than one hour has been found to be sufficient and depends on the total input of mixing energy (such as ultrasonic energy).

Step b): Contacting the product obtained from step a) with an aqueous latex of a second polymer. This second polymer is a polymer constituting a matrix of carbon nanotube reinforced polymer, where carbon nanotubes are It is well distributed. Any aqueous polymer latex known to those skilled in the art can be used. Second polymers include polyacrylates, styrene-based (co) polymers, butadiene-based (co) polymers, polycarbonates, acrylonitrile-based (co) polymers, (halogen-containing) polyolefins (polyethylene or polypropylene, homo and copolymers), and polyamides. Preferably selected from the group. The second polymer may be polystyrene or a copolymer of olefin or styrene and either (meth) acrylate, maleic anhydride, maleimide, 2- or 4-vinylpyridine, acrylonitrile, or another vinyl or vinylidene type monomer. Use is further preferred.

  In order to achieve the benefits of the present invention, the second polymer has both a low molar mass fraction and a high molar mass fraction, the low molar mass fraction having a weight average molecular weight (Mw) of 500-20,000 g / mol. The high molar mass fraction should have a Mw of 20,000 to 5,000,000 g / mol. The amount of low molar mass fraction in the second polymer is greater than 5 wt%. More preferably, this amount is at least 6.5 wt%. The low molar mass fraction is also generally present in equal or lesser amounts, more preferably up to 40 wt% of the second polymer.

  The low molar mass fraction may be based on the same monomer as the high molar mass fraction, but the monomers for that fraction may also be different from each other. Preferably, the second polymer is a composition of two miscible polymers based on either different monomers or the same monomer, one polymer forming a low molar mass fraction and the other polymer having a high A molar mass fraction is formed.

  The composition of the second polymer can be obtained in various ways, either during polymerization with the second polymer or by mixing with the polymerization product. In the first preferred embodiment, a broad molar mass distribution is produced that includes both low Mw polymers (500-20,000 g / mol Mw) and high Mw polymers (20,000-5,000,000 g / mol Mw). By applying polymerization conditions, a second polymer is obtained. In a second preferred embodiment, the second polymer is obtained by mixing a low Mw polymer and a high Mw polymer. The conditions under which polymerization with the second polymer needs to occur depend on the type of second polymer used. In essence, once the type of second polymer is selected, one skilled in the art knows how to produce a low molar mass fraction and a high molar mass fraction in the polymerization process, either during one polymerization or in two separate polymerizations. . In the last version, the two separate polymerization products are mixed together in the desired ratio.

  The temperature of the mixing step b) is generally 10 to 150 ° C. The atmospheric pressure is generally atmospheric pressure, but may be increased to adjust the processability in this step b) or the next step c). The residence time in this step b) is not critical and generally does not exceed 1 hour.

Step c): A step of treating the mixture obtained in method step b) to remove (substantially all) water There are different physical methods available to the person skilled in the art to achieve this removal. Of these methods, step c) is preferably performed by evaporation, freeze drying, or air flow drying.

Step d): Preparation of a homogeneous dispersion of CNTs in the second polymer If the second polymer is a thermoplastic polymer, the temperature in this step d) is the melting point (in the case of a (semi) crystalline second polymer) or glass It is selected to be 10 to 100 ° C. higher than the transition temperature (in the case of the liquid crystal second polymer). In all cases, the person skilled in the art knows that the process conditions under which this step d) is carried out depend on the nature of the second polymer chosen.

Step e): Solidification of the product of step d) into the desired form This step e) is a molding step, pellet molding step, extrusion molding, injection molding or compression molding to form a solidified polymer object. It may be a step or any known step.

  By the method of the present invention, a CNT reinforced polymer is obtained. The CNTs are essentially dispersed individually in the polymer matrix. Therefore, the polymer has improved stiffness and better conductive properties.

  The present invention also relates to a carbon nanotube reinforced polymer that can be obtained by the method of the present invention. According to the present invention, a polymer composite having a conductive percolation threshold with 3 wt% or less of CNTs can be obtained. In particular, the method of the present invention provides a product having a resistivity of less than 100 Ω × cm with an amount of carbon nanotubes of less than 3 wt%. In the art, such resistivity is achieved only at very high CNT addition, Mater. Sci. 37, 2002, pages 3915-23.

  In the present invention, it has generally been found that the amount of low mass fraction in the second polymer is not included in an amount (by weight) that is more than half of the second polymer. Preferably, the weight ratio of the low molar mass portion of the second polymer to the high molar mass portion of the second polymer is 0.065 to 0.67. More preferably, the ratio is 0.10 to 0.25. As mentioned above, as long as the two fractions are compatible and / or miscible with each other, the two fractions may be based on the same monomer, and the two fractions may also be based on different monomers. Depending on the desired stability level of conductivity, the required proportion of low molar mass fraction can be easily determined.

  The reinforced polymer of the present invention can be used in several applications where improved stiffness and conductive properties can be utilized. Examples include shielding applications (such as electromagnetic interference shielding); highly elastic conductor panels for the automotive industry having a surface appearance superior to glass fiber filled polymers; nanoelectronic devices (eg, thin film transistors), etc. .

  The invention is illustrated by the following non-limiting examples.

Materials and technical materials: CNT HIPCO NT (Carbon Nano Technology) (SWNT) and SDS (Merck) were used as they were.

  An aqueous product of CNT + SDS was prepared according to the teachings of WO 02/076888. SDS was dissolved in water at room temperature to form a 0.5 wt% to 15 wt% solution. The generated single-wall nanotube powder containing the rope bundle network was sonicated in very mild conditions (50 W, 43 KHz) for 15-20 minutes in solution (concentration of 0.2 wt% to 3 wt%). . A black, homogeneous ink-like product was obtained, which was mixed with different polystyrene (PS) latex or polypropylene (PP) latex at room temperature. The resulting mixture was then lyophilized overnight (Christ α2-4) to compress the dried powder. Nanocomposites based on PS1 latex, PS2 latex and PS3 latex were molded at 160 ° C. and 10 MPa for 4 minutes (after 4 cycles of degassing). For nanocomposites based on polymer latex PS4 and PS5, after degassing was cycled four times, the dry powder was compression molded by performing 20 seconds twice at 180 ° C. and 4 MPa, and once for 2 minutes at 10 MPa. Nanocomposites based on PP1 latex and PP2 latex were molded at 180 ° C. and 10 MPa for 3 minutes.

Production of PS1-PS2 Latex PS1 is a latex having a broad molecular weight distribution, while PS2 has a narrow molecular weight distribution.

Preparation of polymer latex PS1 Emulsion polymerization was carried out in an oxygen-free atmosphere. 292 g styrene was mixed with 728 g water, 13 g SDS, and 1.1 g NaHCO ₃ as a buffer. The temperature was kept at 50 ° C. The reaction was started with 1 g of SPS (sodium persulfate). The reaction time was 2.5 hours.

  The polymerization was initiated without degassing the reaction mixture, which meant that some oxygen was still dissolved in the reaction mixture, which resulted in the formation of significant amounts of low molecular weight PS species. .

Preparation of polymer latex PS2 A procedure similar to latex PS1 was applied except that the following conditions were followed: 200 g styrene; 695 g water; 13.4 g SDS; 1 g SPS.

  The reaction temperature was kept at 65 ° C. and the reaction mixture was carefully degassed with argon to initiate the polymerization (resulting in the synthesis of PS with essentially high molecular weight chains).

Preparation of PS3 (mixing of PS2 latex and low Mw polystyrene)
Incorporation of low molar mass PS into PS2 latex was accomplished by the following procedure: 130 g PS2 latex was mixed directly with 624 mg SDS, followed by 715 mg PS reference (Mw = 550 g / mol). Using Ultraturrax (Ika, Labotechnic, Janke and Kunkel), the resulting dispersion was subjected to high shear for 3 minutes at minimum speed (4000 rpm).

Preparation of polymer latex PS4 Emulsion polymerization was carried out in an oxygen-free atmosphere (including 2.5 hours of pre-degassing with Ar). First, 252.2 g styrene was mixed with 715 g water, 26 g SDS and 0.5 g Na ₂ CO ₃ . The temperature was kept at 50 ° C. and the reaction was started by injection of 0.7 g SPS dissolved in 7 mL water. The reaction time was 2.5 hours. The resulting latex had a broad molecular weight distribution.

Preparation of Polymer Latex PS5 The experimental procedure for the synthesis of PS5 was similar to the procedure used for the synthesis of PS4. Degassing was performed for 5 hours. 252.04 g of styrene was mixed with 715 g of water, 25.97 g of SDS and 0.45 g of Na ₂ CO ₃ . The temperature was kept at 70 ° C .; the reaction time was 0.5 hours. The resulting latex had a narrow molecular weight distribution.

Materials for producing polystyrene nanocomposites : CNT-HiPCENT (SWNT) and SDS (Merck) purchased from Carbon Nanotechnology were used as they were. An aqueous product of CNT + SDS was prepared as described above.

Preparation of polypropylene nanocomposites Both multi-walled nanotubes (MWNT) and single-walled nanotubes (SWNT) were used in the preparation of these nanocomposites. MWNT was obtained from Nanocyl (Nanocyl-3100); SWNT was HIPCONT obtained from Carbon Nanotechnology. The polypropylenes used were Priex® 801 (maleic anhydride grafted homopolypropylene) and Priex® 701 (maleic anhydride grafted copolymer polypropylene having about 5 wt% ethylene as a comonomer) obtained from Solvay, Both had 29 wt% PP with Mw less than 20,000 g / mol (according to GPC).

  The conductivity measurement was a two-point measurement. The results for Priex® 801 are shown in FIG. 2 as a MWNT composite and in FIG. 3 as a SWNT composite; FIG. 4 shows the results for Priex® 701 with HIPCO-SWNT.

Conductivity measurement Electrical conductivity measurements at room temperature were performed using a DC-Conductivity Keithley 6512 Programmable Electrometer which is either a 2-point or 4-point configuration.

  Measurements were made directly on the membrane surface. Contact between the sample and the measuring device was improved using a colloidal graphite paste provided by Electron Microscience Science (Cat. No. 12660).

  The results of the conductivity measurements are shown in FIG. 1 (for PS1 and PS2 nanocomposites), Table I (for PS2 and PS3 nanocomposites); and Table II (for PS4 and PS5 nanocomposites).

  Conductivity measurement PS1-PS2 curve: 4-point measurement was used. PS2-PS3 comparison of conductivity values: Two-point measurement was used. For PS4 and PS5 measurements: A 4-point measurement was used.

Determination of the amount of low molecular weight PS in the latex Determination of the amount of polymer having a molecular weight of less than 20,000 g / mol (corresponding to an elution time of about 12.5 minutes in GPC analysis using THF as the medium) Performed using the apparatus.

  The amount of PS or PP having a Mw of less than 20,000 g / mol listed in Table III is that of a PS species having a molecular weight comprised between 20,000 g / mol and the Gw-based Mw (ie 550 g / mol). Calculated taking into account the amount.

The result of the conductivity measurement is shown in FIG. 1 (for PS1 nanocomposite and PS2 nanocomposite). The results for Priex® 801 are shown in FIG. 2 as MWNT composites. The results for Priex® 801 are shown in FIG. 3 as SWNT composite. Results are shown for Priex® 701 with HIPCO-SWNT.

Claims (12)

a) contacting a carbon nanotube with a water-soluble component that is a water-soluble first polymer or water-soluble surfactant in an aqueous medium;
b) mixing the product obtained from step a) with an aqueous latex of the second polymer;
c) removing water from the mixture obtained in the previous step;
d) heating the product from step c) to a temperature at which the second polymer flows;
e) a method of preparing a carbon nanotube reinforced polymer by solidifying the product of step d) into a desired form comprising:
The second polymer has both a low molar mass fraction and a high molar mass fraction, the low molar mass fraction has a weight average molecular weight (Mw) of 500 to 20,000 g / mol, and the high molar mass. The fraction of carbon nanotube reinforced polymer having a Mw of 20,000 to 5,000,000 g / mol and the low mass fraction present in the second polymer in an amount greater than 5 wt%. Preparation method.   The second polymer is a composition of two miscible polymers based on either different monomers or the same monomer, one polymer forming the low molar mass fraction and the other polymer being the high polymer. The method of claim 1, wherein a molar mass fraction is formed.   The method according to claim 1, wherein the second polymer is obtained by mixing a low Mw polymer and a high Mw polymer.   Wide molar mass where the second polymer comprises both a low Mw polymer (having a Mw of 500-20,000 g / mol) and a high Mw polymer (having a Mw of 20,000-5,000,000 g / mol) The process according to claim 1, obtained by applying polymerization conditions that produce a distribution.   The said second polymer is a copolymer of styrene and (meth) acrylate, maleic anhydride, maleimide, 2- or 4-vinylpyridine, acrylonitrile, or another vinyl or vinylidene type monomer. The method according to any one of the above.   6. A method according to any one of the preceding claims, wherein the low molar mass fraction is present in the second polymer in an amount of at least 6.5 wt%.   7. A method according to any one of the preceding claims, wherein the low molar mass fraction is present in the second polymer in an amount up to 40 wt%.   The method according to claim 1, wherein single-walled carbon nanotubes are used.   The carbon nanotube reinforcement | strengthening polymer obtained by the method as described in any one of Claims 1-8. The carbon nanotube reinforced polymer according to claim 9, wherein the resistivity is less than 100 Ω ^* cm.   The carbon nanotube reinforced polymer according to any one of claims 9 to 10, wherein the ratio of the low molar mass portion of the second polymer to the high molar mass portion of the second polymer is 0.065 to 0.67. .   The carbon nanotube reinforced polymer according to claim 11, wherein the ratio is 0.10 to 0.25.

Images